Dr Aaron Davis at the Royal Botanic Gardens, Kew, and colleagues from Uganda, reveal new insights into the history of Liberica coffee, and the potential of excelsa coffee as major crop plant in an era of anthropogenic climate change.
Liberica or Liberian coffee (Coffea liberica) is often dubbed the “third coffee crop species”, after Arabica (C. arabica) and robusta (C. canephora). A commonly misquoted statistic is that Liberica constitutes around 1 per cent of global coffee supply, but production output of this species is miniscule compared to Arabica and robusta. However, during the latter part of the 19th century, Liberica stood alongside Arabica as the second most important species of coffee trade.
Liberica was introduced with remarkable scale and efficiency from the early 1870s onwards, initially as a response to the coffee leaf rust epidemic that was devastating Arabica plantations in Ceylon (then Sri Lanka). Soon afterwards, it was used to extend coffee production to low elevation tropical areas where conditions were too hot and too wet for Arabica. Scientists, government officials and growers were particularly impressed by the size and robustness of Liberica: all parts of the plant are larger than Arabica, and it appeared to grow easily and quickly, even in poor, depleted soils. By the early 1880s, it was firmly established in several countries across the coffee belt, and soon afterwards it had become globalised.
Despite this apparent success, the use of Liberica was remarkably short-lived. By the turn of the 20th century it had almost universally fallen out of favour, and its use as a commodity crop came to an abrupt end. But why? Literature of that era shows that Liberica was unpopular with many consumers, who, at best, were unsure about its flavour. It was also generally ill-favoured by coffee traders. Then, in 1897, a new species came along – robusta coffee – which quickly found favour over Liberica, at least from coffee farmers and traders. The downfall of Liberica was concluded by the expansion of Arabica from the late 19th century onwards, particularly in Brazil, which at the time caused plummeting global coffee prices and the reduction or abandonment of Liberica and other coffees as farmers switched to more profitable crops.
Today, as roasters and consumers search for diversification of the coffee experience, and producers look at means of ensuring sustainability and improving profitability, Liberica is seeing something of a revival. The last five years or so, have witnessed much wider retail availability, particularly via online sales. When properly processed, Liberica is praised for its sweet, mild (low to medium acidity, and minimal bitterness), fruit-driven cup profile. It was even showcased at the 2021 World Barista Championships. Regardless, Liberica production and consumption is still a small- scale affair, even in countries such as Malaysia, the Philippines, and parts of Indonesia, where it is often favoured over Arabica and robusta.
In our new research paper, The re-emergence of Liberica coffee as a major crop plant (published in Nature Plants), my colleagues and I suggest that the type of Liberica selected for introduction and upscaling in the 1870s was either a poor choice or a matter of unfortunate circumstance. Most of those early introductions were the large- fruited and large-seeded type of Liberica. Initially, the “bigger is better” principal must have seemed like a good bet, but the thick, tough pulp of the large fruits meant that the coffee was difficult to process, resulting in poor quality and an undesirable coffee. The large coffee beans were also unpopular with merchants and retailers.
Critically, our research highlights a key disadvantage of farming large-fruited Liberica. Due to the thick, tough pulp of the large fruits, it can take up to twice the amount of fresh cherry to produce the equivalent weight of clean coffee compared to Arabica. Unfavourable conversions, otherwise known as the outturn, are critically important for famers because they incur increased costs, particularly for harvesting, transportation, and processing. Income, as well as environmental sustainability, are among the key objectives of our research team, who are working together on a project investigating the wild coffee resources of Uganda, funded by the United Kingdom Government under the Darwin Initiative.
At around the same time as the demise of Liberica as a major crop plant, numerous varieties, and species associated with Liberica were recognised by botanists. Of particular note is excelsa coffee (C. excelsa) from Central and East Africa, which is now mostly regarded as a botanical variety of Liberica (as var. dewevrei). In reports published during the early to mid-20th century, it was praised for high yields at more than 1000 kilograms per hectare of clean coffee, the ability to withstand pruning, resistance to a range of diseases and pests, and tolerance to drought and low temperatures. Importantly, the fruit and seeds were identified as being of an equivalent size to Arabica, which enabled the use of standard protocols for harvesting, drying, processing – and, as I and my colleagues attest, a satisfactory outturn. Much of the excelsa being grown worldwide is not “true” excelsa, but instead smaller fruited/seeded types of Liberica (var. liberica) or possibly hybrids.
In terms of flavour quality, early historical reports for excelsa were promising, as stated by various authors. They described it as “mild and far from the extreme bitterness of Liberica”, “with [a] mild flavour, of fair quality in some strains”, “good quality coffee”, or simply as “good coffee”.
Indeed, in the early to mid-20th century, many agronomists saw great potential in excelsa coffee. Despite these accolades, the use of excelsa never really took off, probably because Arabica and robusta served the coffee sector well enough – until now.
Uganda and South Sudan have recently experienced a localised and yet dramatic upscaling of excelsa. In lowland Uganda, there are at least 200 farms now growing excelsa, and this number is growing year-on- year, mainly by farmers shifting from robusta to mixed robusta-excelsa or excelsa-only. The farming of excelsa in Uganda has been ongoing for perhaps the last 20 years, but appears to have increased dramatically over the last decade or so. The shift appears to be linked to production issues with robusta, and particularly the increasing occurrence and severity of disease and pests, and the changing climate.
Dr. Catherine Kiwuka, from the National Agricultural Research Organization in Uganda, co-author of the research, has witnessed the enthusiasm for excelsa among smallholder farmers.
“Farmers are choosing excelsa coffee because it’s easy to grow, apparently more tolerant to disease and pests than robusta, and is high yielding,” she says. “Each tree is capable of yielding up to around eight kilograms of clean coffee, and very old, ‘mother trees’ can produce in excess of 40 kilograms.”
Independently, South Sudan has recently seen the planting of a large excelsa-only estate, and the establishment of an extensive excelsa outgrowers program, which currently involves more than 1000 smallholders covering more than 200 hectares. The South Sudan project, which is managed by the Equatoria Teak Company, and funded by the Dutch Ministry of Foreign Affairs through the Netherlands Enterprise Agency, is at quite an early stage but the excelsa is proving to be robust, high yielding, and well suited to local conditions.
Ian Paterson, of the Equatoria Teak Company, lives and works on the new excelsa estate in South Sudan. “Excelsa coffee is found naturally in our area, and is proving to be hardy, deep- rooted, and quick growing, with the potential for excellent yields,” he says.
The uptake in Uganda and South Sudan is notable in itself, but there are two other key points. Firstly, the preference to plant excelsa (over robusta, or other coffee) has been farmer-led in both countries, rather than based on advice from either external stakeholders or intervention agents.
Secondly, excelsa is an indigenous plant of Uganda and South Sudan, and the planting stock being used appears to have been taken directly from forest to the farm. Ugandan farmers say that it came from the forest but has been with them for some generations, and only recently used as a crop species.
There is currently no recognised market for excelsa coffee in Uganda. Most of it ends up mixed with robusta. Despite this, Uganda excelsa has been exported in small quantities under the local name of kisansa coffee, by Slow Foods, and a small, dedicated export of excelsa was made to Clifton Coffee Roasters in the UK in 2022. However, significant export volumes are envisaged for Uganda and South Sudan. Kyagalanyi Coffee (Volcafe/ED&F Man) are managing the Ugandan logistics and exports for the Darwin Project.
The key question, however, is what does it taste like? In agreement with historical reports, excelsa produces a sweet, mild, smooth coffee, of low acidity and bitterness, and a range of flavour notes, including various fruits, chocolate, and spices. Some have described excelsa as “the Merlot of the coffee world”. Excelsa and Liberica coffee beans have roughly the same caffeine content as Arabica.
Work is underway to more precisely understand the climate resiliency potential of Liberica and excelsa coffee and assess the level of resistance to various pests and diseases. However, in a changing climate, Liberica and excelsa at the least, offer the potential to grow commercially viable, and perhaps higher- valued coffee under much warmer conditions, and at lower elevations than Arabica, and may offer improved climate resiliency over robusta.
The scale of uptake for Liberica, and particularly excelsa, will largely depend on the performance of Arabica and robusta coffee under climate change, and other factors causing coffee supply chain disruption.
Dr Aaron Davis is Senior Research Leader of Crops and Global Change at the Royal Botanic Gardens, Kew, in the United Kingdom. His research is focused on coffee, and includes the use and development of wild and underutilised coffee species, particularly within the context of climate change adaptation and sensory diversification.
This article was first published in the January/February 2023 edition of Global Coffee Report. To read the research paper, click HERE.